Effect of carbocysteine on cough reflex to capsaicin in asthmatic patients

Aims  Cough, one of the main symptoms of bronchial asthma, is a chronic airway inflammatory disease with functionally damaged bronchial epithelium. Recently, we established an animal model with cough hypersensitivity after antigen challenge and clearly showed the protective effect of carbocysteine in this model. This study was designed to investigate the clinical effect of carbocysteine for cough sensitivity in patients with bronchial asthma. Methods  The effects of the two orally active mucoregulatory drugs, carbocysteine and ambroxol hydrochloride, on cough response to inhaled capsaicin were examined in 14 patients with stable asthma. Capsaicin cough threshold, defined as the lowest concentration of capsaicin eliciting five or more coughs, was measured as an index of airway cough sensitivity. Results  Geometric mean values of the cough threshold at run‐in (baseline) and after 4 weeks’ treatment of placebo, 1500 mg day −1 of carbocysteine and 45 mg day −1 of ambroxol hydrochloride were 12.8 µ M (95% confidence interval [CI] 5.5, 29.6), 11.0 µ M (95% CI 4.4, 27.5), 21.0 µ M (95% CI 8.8, 50.2) and 11.6 µ M (95% CI 5.8, 23.3), respectively. The cough threshold for carbocysteine was significantly greater than those of ambroxol hydrochloride ( P  = 0.047) and placebo ( P  = 0.047), respectively. Conclusions  These findings indicate that carbocysteine administration may be a novel therapeutic option for asthmatic patients, especially with cough variant asthma.